Compressed gas cylinders incorporate one or more fusible plugs embedded in the wall of the cylinder, or cylinder outlet valve, to prevent overpressurization of the cylinder due to overheating. When excessive heat is applied to the compressed gas cylinder, the fusible plug(s) melt before overpressurization can occur and cause the cylinder to rupture. Should a fusible plug melt, or a compressed gas cylinder rupture, potentially harmful gas and liquid in the cylinder will be released to the atmosphere.
As can be seen by reference to U.S. Pat. Nos.: 4,633,061; 4,695,703; 4,695,712; and 4,833,299, the prior art is replete with myriad and diverse patented constructions which provide flexible heating pads.
While the prior art constructions are adequate for the purpose and function for which they were specifically designed, they fall far short of providing the safety and economy of a flexible self-regulating heating pad that is suited to conform to and be removeable from a compressed gas cylinder.
For instance, in the U.S. Pat. No. 4,833,299 of Estes (1989), there is described a flexible heating wrap which includes a plurality of heating elements controlled by individual temperature responsive control devices which are used to regulate the quantity of heat output by the heating wrap.
This present invention utilizes the thermal characteristics of a self-regulating heating element in combination with the physical dimensions of the heating pad, and the heat retaining characteristics of the insulating material to regulate the quantity of heat output to a cylinder. The advantages of using a self-regulating heating element without other separate temperature responsive control devices include safety, as the heating pad can never exceed the melt temperature of the fusible plug(s) in the compressed gas cylinder or cylinder outlet valve; and economy of operation, by virtue of the electrical and thermal operating characteristics of the self-regulating heating element.